404 PEACTICAL PHYSIOLOGY 



similar control vessel. The gauges are graduated in both limbs in 

 millimetres to a height of about 300 mm. 



The limbs of each gauge are connected by wide rubber tubing which 

 can be compressed by a screw clamp so as to adjust the levels. The 

 gauges are filled with water, tinged with methylene blue. One limb 

 of each gauge is provided with a three-way tap close to the top. 

 The blood-gas vessel and the control vessel are of similar form, 

 and each has a capacity of about 20 c.c. The glass stopper of each is 

 perforated by a glass tube of narrow bore which widens below into a 

 pocket capable of holding -3 c.c. The pocket is so arranged that any 

 liquid contained in it can easily be emptied by tilting the vessel. 



The two vessels are connected with the top ends of the two gauges 

 by equal lengths of pressure tubing of narrow bore. This tubing is 

 made as short as possible. The control vessel has a few drops of water 

 in it. 



Before the sample of blood is collected, 1-5 c.c. of ammonia solution 

 (ammonia sp. gr. 0-88, 5 c.c. in 1000 c.c. water) is measured with a 

 pipette into the blood-gas vessel, and -25 c.c. of saturated solution of 

 potassium ferricyanide is placed in the glass pocket. 



The sample of blood 1 c.c. is collected in a hypodermic syringe from 

 the blood vessel; '10 c.c. of ammonium oxalate is first drawn into the 

 syringe. In the syringe there is a glass bead, by means of which the 

 oxalate solution and blood can be mixed, The blood is then dis- 

 charged into the blood-gas vessel beneath the ammonia solution which 

 prevents all contact with air. The blood-gas vessel is then closed and 

 placed in the water bath beside the control vessel. The water is 

 stirred by blowing through it, and the gauges are watched until the 

 pressure, i.e. the temperature, in each vessel becomes the same. The 

 gauges are now adjusted at zero by opening the taps for a moment. 

 The blood-gas vessel is then taken out, and the ammonia solution and 

 blood mixed. When the blood is quite laked, and the solution 

 transparent, the vessel is tilted so as to empty out the ferricyanide, 

 and then shaken to liberate all the oxygen. During these manipula- 

 tions the blood-gas vessel is held in a cloth to prevent warming. It is 

 now replaced in the water bath, and the water is stirred. When the 

 temperature has again become even, the gauges are adjusted so that 

 the levels in the limbs connected with the bottles are at zero. The 

 heights on the other limbs are read off, and if, as is usual, the tempera- 

 ture has risen, so that the level is higher than before in the open limb 

 of the control vessel gauge, the reading of this gauge is deducted from 

 the reading of the other gauge. The temperature of the water bath is 

 now read. The normal barometric pressure equals 10,300 mm. H 2 0. 



